The invention relates to a method for the production of lignocellulose-based products by modifying lignocellulosic material (for example wood). The invention also relates to products which are produced by this method, for example composite materials.
Various methods for enzymatic modification of lignocellulosic material are known from the prior art. Thus EP 0772 717 B1 discloses a method for treating lignocellulosic material and a phenolic polysaccharide with an enzyme which is capable of catalysing the oxidation of the phenol groups in the presence of an oxidising agent. The phenolic polysaccharide comprises substituents which contain phenolic hydroxyl groups. In this case the phenolic polysaccharide is added to the lignocellulosic material and does not, for instance, form an original constituent of the lignocellulosic material. Thus a method for enzymatic coupling of additives (preferably phenols of any sort) is described in this document, with the additives functioning separately as binders. The additive thus replaces conventional binders, such as aminoplasts, phenoplasts, isocyanates, polyvinyl acetates, epoxy resins or acrylic resins.
DE 36 21 218 A1 describes a method for producing a binder for wood- or cellulose-containing materials by using lignin compounds where the lignin compounds are mixed with exopolysaccharides. The exopolysaccharides are obtained in a separate method step by microorganisms in suitable nutrient media (culture fluids). What is involved here is a binder produced by enzymatic reactions which is then added to the wood- or cellulose-containing materials (substrate). The document does not describe an enzymatic and/or chemical reaction between the substrate and the binder.
DE 43 31 878 A1 and WO 99/31155 describe methods for producing polymers which contain lignin and organic compounds and polymers produced by the methods where the organic compounds comprise at least three carbon atoms. The lignin used as the initial material can be natural plant lignin, obtained from wood for example, but in particular sulphite lignin or alkali lignin (kraft lignin) as occurs in large quantities with chemical pulping for industrial production of cellulose. Peroxidases (for example manganese peroxidase) and phenol oxidases (for example laccases, tyrosinases) can be used as the radically oxidising enzymes, which together with oxidising agents, such as hydrogen peroxide or oxygen, induce polymerisation. WO 99/31155 cites numerous applications for the polymer obtained, inter alia the use of polymers of this type to cure wood materials. These documents do not disclose an enzymatic and/or chemical reaction between wood material and polymer (binder).
U.S. Pat. No. 6,187,136 B1 describes a method for producing modified lignin by enzymatic coupling of phenols to lignin. Fundamental to the method described is that the phenols carry positively or negatively charged functional groups, so an ionic interaction of oppositely charged functional groups takes place. In other words, a covalent bond between enzymatically applied additive and the binder is not sought. The described method allows improvement to the binding properties in the course of paper production when using a charged binder, such as cationic starch and negatively charged lignocellulose. The particular drawback of the method is that conventional binders, as are used for example for the production of wood materials, cannot be used.